Implantable hearing aids entail the subcutaneous positioning of some or all of various hearing augmentation componentry on or within a patient's skull, typically at locations proximate the mastoid process. Implantable hearing aids may be generally divided into two classes, semi-implantable and fully implantable. In a semi-implantable hearing aid, components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit a processed audio signal to implanted components such as a receiver and transducer. In a fully implantable hearing aid, typically all of the components, e.g., the microphone, signal processor, and transducer, are located subcutaneously. In either arrangement, a processed audio signal is provided to a transducer to stimulate a component of the auditory system.
By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to mechanically stimulate the ossicles via physical contact. (See e.g., U.S. Pat. No. 5,702,342.) Generally, such a vibratory actuator is mechanically engaged (i.e., coupled) with the ossicles during mounting and positioning of the transducer within the patient. In one example, such coupling may occur via a small aperture formed in the incus bone that is sized to receive a tip of the electromechanical transducer. In such an arrangement, the transducer tip may expansively contact the sides of the aperture, may be adhered within the aperture or tissue growth (e.g., osteointegration) may couple the transducer tip to the bone. One disadvantage of methods requiring a hole in the ossicle to facilitate attachment is that a surgical laser must be employed to ablate the ossicle's surface. The laser ablation procedure is burdensome and time consuming. Also, the required equipment is expensive and not present in every surgical setting. In other arrangements, clamps and/or clips are utilized to couple the vibratory actuator to an ossicle. However, such approaches can entail difficult implant procedures and yield sub-optimum coupling.
As will be appreciated, coupling with the ossicles poses numerous challenges. For instance, during positioning of the transducer, it is often difficult for an audiologist or surgeon to determine the extent of the coupling, or in other words, how well the actuator is attached to the ossicles. Additionally, due to the size of the transducer relative to the ossicles, it is difficult to determine if loading exists between the ossicles and transducer. For example, precise control of the engagement between the actuator of the transducer and the ossicles is of critical importance as the axial can only be effectively communicated when an appropriate interface or load condition exists between the transducer and the ossicles. Overloading or biasing of the actuator can result in damage or degraded performance of the biological aspect (e.g., movement of the ossicles) as well as degraded performance of the mechanical aspect (e.g., movement of the vibratory member). Additionally, an underloaded condition, i.e., one in which the actuator is not fully connected to the ossicles, may result in reduced performance of the transducer. In addition, once coupled for an extended period, the maintenance and/or replacement with a next generation transducer may be difficult. That is, in many coupling arrangements it may be difficult to de-couple a vibratory actuator/transducer.